Discharge device for the bottom fraction at a vortex type separator

ABSTRACT

A device is provided for discharging the heavy bottom or reject fraction from a vortex type separator. The device comprises a vortex chamber disposed underneath the bottom fraction outlet of the separator with the axis of symmetry of the vortex chamber parallel to the axis of symmetry of the bottom fraction outlet. The vortex chamber is provided with a stationary outlet port for the reject fraction, located in the circumferential wall of the vortex chamber or in the bottom of the vortex chamber close to the circumferential wall thereof. The vortex chamber is displaceable relative to the bottom fraction outlet in a direction perpendicular to the axis of symmetry of the vortex chamber. By displacing the vortex chamber relative to the bottom fraction outlet of the separator it is possible to vary the flow volume of the bottom fraction being discharged through the outlet port of the vortex chamber.

HI States Patent 1 1 Skardal 1 51 May 22, 1973 Karl Arvid Skardal, Artillerigatan 48, 114 45 Stockholm, Sweden Filed: Mar. 11, 1971 Appl. No.: 123,280

Inventor:

[30] Foreign Application Priority Data Mar. 12, 1970 Sweden ..3314/70 Great Britain ..209/21 1 Primary Examiner-Frank W. Lutter Assistant Examiner-Ralph J. Hill Attorney-Waters, Roditi, Schwartz & Nissen [57] ABSTRACT A device is provided for discharging the heavy bottom or reject fraction from a vortex type separator. The device comprises a vortex chamber disposed underneath the bottom fraction outlet of the separator with the axis of symmetry of the vortex chamber parallel to the axis of symmetry of the bottom fraction outlet. The vortex chamber is provided with a stationary outlet port for the reject fraction, located in the circumferential wall of the vortex chamber or in the bottom of the vortex chamber close to the circumferential wall thereof. The vortex chamber is displaceable relative to the bottom fraction outlet in a direction perpendicular to the axis of symmetry of the vortex chamber. By displacing the vortex chamber relative to the bottom fraction outlet of the separator it is possible to vary the flow volume of the bottom fraction being discharged through the outlet port of the vortex chamber.

9 Claims, 5 Drawing Figures Patented May 22, 1973 5 Shoots-Sheet 1 Patented May 22, 1973 3,734,288

3 Shoots-Sheet 2 Patented May 22, 1973 3,734,288

3 Shouts-Sheet 3 C mm Flg

Q Q Q Q l/min DISCHARGE DEVICE FOR THE BOTTOM FRACTION AT A VORTEX TYPE SEPARATOR This invention relates to a device for discharging the heavy bottom or reject fraction from a vortex type separator used for the separation of solid material suspended in a liquid, in particular vortex type separators for cellulose fiber slurries, with rejection of a bottom or reject fraction having a comparatively high density.

Vortex type separators of this type are generally provided with a discharge chamber for the reject fraction, which is connected to a bottom outlet for the reject fraction in the conical part of the separator. In order to prevent the reject fraction and possibly also air from being resucked into the separator through its bottom outlet said discharge chamber is generally designed as a vortex or whirl chamber, which is provided with an outlet port for the reject fraction and in which the reject fraction forms a vortex flow with a comparatively high flow velocity.

At the operation of a separator provided with such a discharge device for the reject fraction, however, the control of the liquid volume containing the reject fraction and being discharged through the bottom fraction outlet of the separator constitutes a major problem. The liquid volume being discharged through the bottom fraction outlet of the separator must be controllable very accurately within a very wide range, as a too large liquid flow through the bottom outlet of the separator causes loss of useful product, whereas-on the other hand a too small liquid flow through the bottom outlet of the separator causes that the reject fraction will partially remain in the separator and be withdrawn therefrom together with the useful product and thus contaminate this. Consequently, it must be possible to reduce the liquid flow being discharged from the bottom fraction outlet of the separator through the vortex chamber down to a very small volume, and this must be possible without any clogging of the outlet port of the vortex chamber or the discharge pipe connected thereto with the solid material suspended in the liquid.

It is known in the prior art to locate the outlet port of the vortex chamber in the circumferential wall of the chamber and to provide a control valve in the discharge pipe connected to this outlet port for the control of the liquid volume being discharged. In such an arrangement, however, the control valve or the discharge pipe respectively are easily clogged by solid material, when the valve is in a position for the most optimum discharge t'low with respect to the desired separation of reject fraction and useful product. Such clogging means of course an interruption in the operation of the separator. In order to overcome this disadvantage it has been suggested in the prior art, e.g., as described in U.S. Pat. No. 3,277,926, to locate the outlet port of the vortex chamber eccentrically in the chamber and displaceable therein in such a way that the radial distance between the outlet port and the center of the vortex chamber can be varied. By variation of the radial distance between the outlet port and the center of the vortex chamber it is then possible to vary the liquid volume being discharged through the outlet port. Although this arrangement eliminates to a substantial extent any clogging of the outlet port and the discharge pipe with solid material, the arrangement has the serious disadvantage, however, that heavy and hard particles, e.g., of the kind that may be found in mechanical wood pulp, will remain in the vortex chamber for a considerable time and give cause to a considerable wear on the walls of the vortex chamber.

In still other prior art devices, described for instance in U.S. Pat. application Ser. No. 838,891, now U.S. Pat. No. 3,578,786, the outlet port of the vortex chamber is located in the circumferential wall of the chamber or close thereto and an adjustable flow guiding member is disposed within the vortex chamber for deflecting the vortex flow away from the outlet port to an extent dependent on the position of the member, whereby a variable liquid volume can be discharged through the outlet port. These devices have given excellent results in that they do not cause any clogging of the outlet port of the vortex chamber or of the discharge pipe and in that hard and heavy particles will not remain in the vortex chamber for any considerable duration so as to give cause to wear on the walls of the chamber. However, it turned out that the adjustable flow deflecting member in the vortex chamber is subjected to a comparatively heavy wear due to cavitation erosion. To provide said member with a wear resistant surface layer, e.g., a chromium layer, is a comparatively expensive step due to the rather complicated shape of the member.

The object of the present invention is therefore to provide an improved device for controlling the volume of the reject fraction being discharged from a vortex type separator, which device is of the type initially described in this specification, comprising a vortex chamber disposed underneath the bottom fraction outlet of the separator chamber and provided with an outlet port in its circumferential wall or in its bottom close to the circumferential wall, but which does not suffer from the above discussed disadvantages of previously used devices of the same type.

In the device according to the invention the above object is achieved in that the vortex chamber has its axis of symmetry parallel to the axis of symmetry of the bottom fraction outlet from the separating chamber of the vortex separator and is displaceable relative to said bottom fraction outlet in a direction perpendicular to said axes of symmetry. Preferably the vortex chamber is displaceable in a direction parallel to the diameter in the vortex chamber, at one end of which the outlet port of the vortex chamber is located. According to one embodiment of the invention the vortex chamber is cylindrical, in which case the maximum flow volume of the reject fraction being discharged through the outlet port of the vortex chamber is obtained with the vortex chamber in such a position that its axis of symmetry substantially coincides with the axis of symmetry of the bottom fraction outlet from the separating chamber. In another and preferred embodiment of the invention the vortex chamber is conical and has its larger end facing the bottom fraction outlet from the separating chamber of the vortex separator, in which case the minimum flow volume of the reject fraction being discharged through the outlet port of the vortex chamber is obtained with the vortex chamber in such a position that its axis of symmetry substantially coincides with the axis of symmetry of the bottom fraction outlet from the separating chamber.

With a device according to the invention and in particular a device with a conical vortex chamber it is possible to control very accurately the liquid flow being discharged through the outlet port of the vortex chamher down to very small flow volumes and even down to a complete interruption of the flow. No risk exists that the outlet port of the vortex chamber or the .discharge pipe connected thereto shallbecome clogged, as the cross-sectional flow area of the outlet port as well as of the discharge pipe remains unrestricted. Further, as the outlet port is located in the circumferential wall of the vortex chamber or close thereto, there is no risk that hard and heavy particles shall remain in the vortex chamber for any substantial time and give cause to wear on the walls of the vortex chamber. The device is of a very simple construction and very inexpensive to manufacture, as the vortex chamber has a very simple shape and does not include any adjustable or movable members. The problems with cavitation within the vortex chamber are also much smaller and due to the simple form of the vortex chamber the walls of the chamber can be provided with a wear resistant surface layer at a comparatively low cost.

In the following the invention will be further described with reference to the accompanying drawings, which show by way of example some embodiments of the invention. In the drawings FIG. 1 shows schematically and in axial section a first embodiment of the invention having a cylindrical vortex chamber;

FIG. 1a is a partial showing of a modified embodiment of the invention, similar to that of FIG. 1;

FIGS. 2 and 3 show schematically and in axial section an especially preferred embodiment of the invention having a conical vortex chamber, FIG. 2 showing the vortex chamber in a position for minimum flow volume through the outlet port of the vortex chamber, and FIG. 3 showing the vortex chamber in a position for a large flow volume through the outlet port; and

FIG. 4 is a diagram showing the flow volume through the outlet port of the vortex chamber as a function of the displacement of the vortex chamber, on the one hand in the device illustrated in FIG. 1 and on the other hand in the device illustrated in FIGS. 2 and 3.

FIG. 1 shows schematically the lower portion of a vortex type separator I having a conical separating chamber 2, a circular bottom fraction outlet 3 for the reject fraction at the lower end of the separating chamber, and a bottom flange or ring 4. A vortex chamber body 6 with a cylindrical vortex chamber is mounted underneath the bottom fraction outlet 3 from the separating chamber 2 in a manner known per se in the art. The vortex chamber 5 has an outlet port 7 in its circumferential wall. A discharge pipe 8 is connected to said outlet port 7.

As shown in the partial view of FIG. 1a, alternatively an outlet port 7a can also be located entirely or partially in the bottom of the vortex chamber 5, in a body 6a, close to the circumferential wall of the chamber, and having a discharge pipe 8a connected to said port.

For variation and control of the flow volume of the reject fraction being discharged through the outlet port 7 or 7a of the vortex chamber the respective body 6 or 6a of the vortex chamber 5 is, in accordance with the invention, displaceable in the direction indicated by an arrow 9 perpendicularly to its axis of symmetry 10 relative to the bottom fraction outlet 3 of, the separator. The vortex chamber body 6, 6a is mounted on the lower side of the bottom flange 4 of the separator by means of a yoke 11 and a clamping screw 12 passing through a threaded hole in the yoke. A seal ring 13 is provided for the necessary sealing between the vortex chamber body 6, 6a and the bottom flange 4.

For the displacement of the vortex chamber body 6, 6a and thus the variation of the distance c between the axis of symmetry 10 of the vortex chamber and the axis of symmetry 14 of the bottom fraction outlet 3 of the separator an adjustment screw 15 is provided, which is screwed into a threaded bore 16 in the vortex chamber body and is rotatably mounted in a bracket arm 17 attached to the yoke 11.

By variation of the distance 0 between the axis of symmetry 10 of the vortex chamber 5 and the axis of symmetry 14 of the bottom fraction outlet 3 it is possible to vary the flow volume of the reject fraction being discharged through the outlet port 7 or 7a of the vortex chamber. As illustrated by the curve A in FIG. 4, the maximum flow volume through the outlet port is obtained when the vortex chamber 5 is positioned exactly underneath the bottom fraction outlet 3 of the separator, i.e., when the axis of symmetry 10 of the vortex chamber 5 substantially coincides with the axis of symmetry 14 of the bottom fraction outlet 3. The more the vortex chamber 5 is laterally displaced from this position, i.e., the larger 0 is made, the smaller the liquid flow through the outlet port 7, 7a of the vortex chamber becomes.

The curve A in FIG. 5 illustrates the results when testing a device of the type illustrated in FIG. 1, in which the vortex chamber 5 as well as the bottom fraction outlet 3 of the separator had a diameter of 30 mm and in which the suspension to be separated was supplied to the inlet of the separator at the upper end thereof (not shown in the drawing) under a pressure of 26 m H 0 and the useful or top fraction was withdrawn from the upper end of the separator under a pressure of 2 m H O.

The mechanism making the above described variation of the discharge flow possible is not quite clear. However, a plausible explanation is that the more the vortex chamber 5 is laterally displaced relative to the bottom fraction outlet 3, i.e., the larger c becomes, the closer the outlet port 7, 7a of the vortex chamber comes to the core 18 of low pressure of vacuum which is formed in the center of the separating chamber 2 and which extends downwards into the vortex chamber 5, whereby consequently the pressure at the outlet port 7, 7a of the vortex chamber becomes lower.

The embodiments of the invention illustrated in FIGS. 1 and 1a and described in the foregoing have generally given very good results in operation and do not suffer from any of the disadvantages discussed in the foregoing that are present in the prior art devices. It has turned out, however, that in the invention it is difficult, even with a very large displacement c of the vortex chamber 5, to reach a very small liquid flow through the outlet port 7 or 7a vortex chamber. This fact is also illustrated by the curve A in FIG. 2. In this respect much better results have been obtained with the embodiment of the invention illustrated in FIGS. 2 and 3, wherefore this embodiment is considered as especially advantageous.

The device according to the invention illustrated in FIGS. 2 and 3 is in essential parts designed in the same manner as the devices illustrated in FIG. 1, la, wherefore corresponding parts are provided with the same reference numerals in FIGS. 2 and 3 as in FIG. 1. The important difference consists therein that a vortex chamber 19, used in lieu of chamber 5, is not cylindrical but conically tapered with its smaller end facing downwards. This difference causes a very unexpected change in the mode of operation of the device in FIGS. 2 and 3 as compared with the mode of operation of the devices in FIGS. 1, 1a.

The curve B in FIG. 4 illustrates the relationship between the flow volume through the outlet port 7 of the vortex chamber 19 and the lateral displacement 0 between the axis of symmetry 10 of the vortex chamber and the axis of symmetry 14 of the bottom fraction outlet 3 for the device illustrated in FIGS. 2 and 3, As illustrated by this curve, a device designed in accordance with FIGS. 2 and 3 gives a minimum liquid flow through the outlet port 7 of the vortex chamber 19, when the vortex chamber 19 is positioned directly underneath the bottom fraction outlet 3, whereas an increasing liquid flow through the outlet port 7 is obtained when the lateral displacement c of the vortex chamber 19 is increased.

The reason for this difference in operation is not quite clear. A possible explanation is that in the conical vortex chamber 19 the centrifugal forces appearing at the conical wall of the vortex chamber produce a pressure component which is directed upwards and which counteracts the downwards directed pressure from the heavier reject fraction which is present closest to the circumferential wall of the separating chamber 2 and the vortex chamber 19, whereby this reject fraction is prevented from flowing downwards into the vortex chamber 19 and out through the outlet port 7. When the vortex chamber 19 is displaced laterally, as illustrated in FIG. 3, these conditions are changed in that the bottom flange of the separator will cover an increasing portion of the vortex chamber 19.

As illustrated by the curve B in FIG. 4, it is quite possible in a device in accordance with FIGS. 2 and 3 to interrupt completely the liquid flow through the outlet port 7 of the vortex chamber 19. The tests, from which the curve B resulted, showed even that with the vortex chamber 19 positioned directly underneath the bottom fraction outlet 3 of the separator, i.e., in the position illustrated in FIG. 2, a vacuum was in fact produced at the outlet port 7, whereby air was sucked into the vortex chamber through the outlet port. A discharge flow through the outlet port 7 of the vortex chamber did not start until the vortex chamber 19 was displaced a little more than 2 mm. The shape of the control curve will of course be dependent on the conicity of the vortex chamber 19. The curve B in FIG. 4 was obtained with a device according to FIGS. 2 and 3, in which the larger diameter of the conical vortex chamber 19 and the diameter of the bottom outlet 3 of the separator was 30 mm and the conical wall of the vortex chamber formed an angle of 30 with the axis of symmetry of the vortex chamber. During the test the suspension to be separated was supplied to the inlet of the separator at the upper end thereof under a pressure of 26 m H 0 and the useful or top fraction was withdrawn from the upper end of the separator under a pressure of 2 m The experiments and tests showed also that if in a device according to FIGS. 2 and 3 the vortex chamber 19 was displaced in an opposite direction to that illustrated in FIG. 3, also this produced an increasing liquid flow through the outlet port 7 of the vortex chamber. However, the shape of the control curve in this case was not quite identical with the shape of the control curve for a displacement of the vortex chamber 19 in the direction illustrated in FIG. 3.

In the embodiments of the invention described in the foregoing the lateral displacement of the vortex chamber is substantially parallel to the diameter in the vortex chamber, at the one end of which the outlet port of the vortex chamber is located. However, also a lateral displacement of the vortex chamber in another direction gives a similar result, in particular for a conical vortex chamber.

I claim:

1. A device for discharging a heavy bottom fraction from a vortex type separator, comprising a vortex chamber disposed underneath and in flow communication with a bottom fraction outlet from the separator, with the axis of symmetry of said vortex chamber parallel to the axis of symmetry of said outlet, said vortex chamber being provided with an outlet port provided in the area of the circumferential wall of said vortex chamber, and means for displacing said vortex chamber relative to said outlet in a direction substantially perpendicular to said axis of said symmetry of the vortex chamber, whereby the flow volume of the bottom fraction being discharged through said outlet port can be varied by displacing said vortex chamber in said direction.

2. The device as defined in claim 1, wherein said outlet port is located in said circumferential wall of the vortex chamber.

3. The device as defined in claim 1, wherein said outlet port is located in the bottom of said vortex chamber close to said circumferential wall.

4. The device as defined in claim 1, wherein said vortex chamber is displaceable relative to said outlet in a direction which is parallel to the diameter in said vortex chamber, at one end of which said outlet port is located.

5. The device as defined in claim 1, wherein said vortex chamber is cylindrical.

6. The device as defined in claim 5, wherein the diameter of said vortex chamber is substantially equal to the diameter of said outlet.

7. The device as defined in claim 1, wherein said vortex chamber is conical and has its larger end facing said outlet.

8. The device as defined in claim 7, wherein said vortex chamber has a diameter at its larger end substantially equal to the diameter of said outlet.

9. The device as defined in claim 7, wherein the conical circumferential wall of said vortex chamber forms an angle of about 30 to said axis of symmetry of the vortex chamber.

l III I 

1. A device for discharging a heavy bottom fraction from a vortex type separator, comprising a vortex chamber disposed underneath and in flow communication with a bottom fraction outlet from the separator, with the axis of symmetry of said vortex chamber parallel to the axis of symmetry of said outlet, said vortex chamber being provided with an outlet port provided in the area of the circumferential wall of said vortex chamber, anD means for displacing said vortex chamber relative to said outlet in a direction substantially perpendicular to said axis of said symmetry of the vortex chamber, whereby the flow volume of the bottom fraction being discharged through said outlet port can be varied by displacing said vortex chamber in said direction.
 2. The device as defined in claim 1, wherein said outlet port is located in said circumferential wall of the vortex chamber.
 3. The device as defined in claim 1, wherein said outlet port is located in the bottom of said vortex chamber close to said circumferential wall.
 4. The device as defined in claim 1, wherein said vortex chamber is displaceable relative to said outlet in a direction which is parallel to the diameter in said vortex chamber, at one end of which said outlet port is located.
 5. The device as defined in claim 1, wherein said vortex chamber is cylindrical.
 6. The device as defined in claim 5, wherein the diameter of said vortex chamber is substantially equal to the diameter of said outlet.
 7. The device as defined in claim 1, wherein said vortex chamber is conical and has its larger end facing said outlet.
 8. The device as defined in claim 7, wherein said vortex chamber has a diameter at its larger end substantially equal to the diameter of said outlet.
 9. The device as defined in claim 7, wherein the conical circumferential wall of said vortex chamber forms an angle of about 30* to said axis of symmetry of the vortex chamber. 